1. Field of the Invention
The present invention relates to a method of producing 4,4xe2x80x2-biphenol, more specifically a method of producing 4,4xe2x80x2-biphenol with high efficiency and yield, in which 3,3xe2x80x2,5,5xe2x80x2-tetra-t-butyl-4,4xe2x80x2-biphenol is sequentially debutylated under relatively mild reaction conditions using reaction bathes arranged in series for two or more steps.
2. Description of the Related Art
4,4xe2x80x2-Biphenol (hereinafter referred to as BP) can be obtained by a debutylation reaction of 3,3xe2x80x2,5,5xe2x80x2-tetra-t-butyl-4,4xe2x80x2-biphenol (hereinafter referred to as TBBP) and has been utilized as a raw material for liquid crystal polymers, super engineering plastics, and the like.
Conventionally, as a method for producing BP by a debutylation reaction of TBBP, a process by batch reaction is known (for example, see Japanese Patent Publication Laid-open No. 63-301837). A debutylation reaction of TBBP in the presence of an acid catalyst takes place sequentially and tri-t-butylbiphenol, di-t-butylbiphenol, mono-t-butylbiphenol and 4,4xe2x80x2-biphenol are produced one by one in this order; however, the rate of the debutylation reaction decreases with the decrease in the number of t-butyl groups. In particular, in order to debutylate mono-t-butylbiphenol with high yield, severe reaction conditions, such as a reaction temperature as high as 250xc2x0 C. or higher and an extended reaction time, have to be used. Further, since a finally produced BP has an extremely low solubility in a reaction solvent, deposition of the product in the reaction solvent has to be controlled, for example, by using a large volume of the reaction solvent.
On the other hand, since generally a sequential process is economically advantageous over a batch process in industrial production of a large amount of chemicals, a sequential process for producing BP has been already suggested, in which TBBP is debutylated in a reaction solvent using serially arranged reaction bathes for multiple steps (for example, see Japanese Patent Publication Laid-open No. H05-331087). Thus, the abovementioned problem associated with sequential reactions has to be solved also in the sequential debutylation reaction of TBBP using serially arranged reaction for multiple steps. Accordingly, in the abovementioned method, a substituted aromatic hydrocarbon such as diethylbenzene is used as a reaction solvent and an acid catalyst is added in portions to each of the reaction bathes for multiple steps in an attempt to solve the abovementioned problem associated with sequential reactions.
However, according to the abovementioned method, as mentioned above, the catalyst has to be added in portions to each of the reaction bathes for multiple steps, which makes the reaction and operation complicated. Further, coloring impurity remains in the reaction product due to the catalyst used, which requires a purification process such as washing of the resulting reaction mixture with an alcohol mixture solvent after completing the reaction. Moreover, in the abovementioned method, when crude (unpurified) TBBP containing butylphenols, which is a reaction mixture of oxidation coupling reaction from 2,6-di-t-butylphenol, is used as a raw material, the reaction solvent becomes a mixture of butylphenols and a substituted aromatic hydrocarbon such as diethylbenzene, which also complicates fractionation and recovering of the solvent after the reaction.
An object of the present invention is to solve the abovementioned problem in the sequential debutylation reaction of TBBP using serially arranged reaction bathes for multiple steps and provide a method of sequentially producing 4,4xe2x80x2-biphenol under relatively mild reaction conditions with improved production yield and efficiency.
According to the present invention, there is provided a method of producing 4,4xe2x80x2-biphenol characterized in that a solvent for addition to a reaction bath for the latter step has a smaller average number of alkyl groups than a solvent for addition to a reaction bath for the former step in the method of producing 4,4xe2x80x2-biphenol in which using serially arranged reaction bathes for two or more steps, a debutylation reaction of 3,3xe2x80x2,5,5xe2x80x2-tetra-t-butyl-4,4xe2x80x2-biphenol is sequentially carried out in the presence of an acid catalyst in a reaction solvent by supplying at least one kind of phenols selected from phenol, monoalkylphenols, dialkylphenols, and trialkylphenols (the number of carbon atoms of alkyl groups in alkylphenols, including these monoalkylphenols, dialkylphenols, and trialkylphenols, is each independently in the range of 1 to 4) in a proportion of at least 0.5 mole part to one mole part of material, i.e., 3,3xe2x80x2,5,5xe2x80x2-tetra-t-butyl-4,4xe2x80x2-biphenol, to each reaction bath as the solvent for addition.